<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Document</title>
  <style>
    body {
      margin: 0 auto;
      padding: 0;
    }
    #pn {
      background-color: #ccc;
      width: 950px;
      display: block;
      margin: 0 auto;
      padding: 5px;
      box-sizing: border-box;
      height: auto;
      text-align: center;
    }
    .content {
      margin: 0 auto;
      padding: 10px;
      box-sizing: border-box;
      width: 950px;
      background-color: gray;
      text-align: center;
      height: 80px;
      color: #fff;
    }
  </style>
</head>
<body>
  <div id="pn">
    <h1>欢迎来到慕课网</h1>
    <h2>大幅广告</h2>
  </div>
  <div class="content">
    <h3>慕课网欢迎你</h3>
  </div>
</body>
</html>